This invention refers to a process for purifying silica sand and, more particularly, to a process for the elimination of iron, aluminosilicates and other soft-type mineral particles or stains such as carbonates, sulfates and clay from silica sand particles.
Sand particles are normally contaminated with iron, aluminosilicates and other soft-type mineral particles and stains, which have to be removed for particular uses in the glass, ceramic and other product manufacturing.
One of the most difficult impurities to release from the sand particles is the iron compound normally staining said particles.
There are some methods for the elimination of iron stains from the sand particles, including transforming the iron impurities into soluble iron salts by treatment with a chemical agent such as concentrated sulfuric acid or some alkalies, and then mechanically attritioning said particles to remove said salts therefrom.
U.S. Pat. Nos. 4,405,588 and 4,401,638 (corresponding to Mexican patents 159,830 and 159,831) of Caballero et al, each respectively disclose a process for removing impurities from silica sand particles, involving several steps of attrition and a chemical attack or lixiviation step which requires a relatively great amount of water and chemical reagents such as concentrated sulfuric acid, to remove said iron stains from said sand particles.
Said chemical attack combined with said attrition steps, were absolutely necessary in said processes because of the characteristics of the attrition which were not and could not be vigorous enough in the existing methods as to remove the persistent iron stains.
Additionally, together with the sand, there are also independent hard particles of aluminosilicate which, in the previous processes, were only polished and diminished in size by said attrition steps to be subsequently eliminated by additional flotation or screening steps.
It was therefore highly desirable to simplify the process by reducing at the minimum the number of attrition steps and also by suppressing the chemical attack and suppressing or at least reducing at the minimum the consumption of water in said attrition step.
Such simplification in the process for purifying silica sand is now possible in accordance with the present invention, by providing a new abrasive-attrition step in which the sand particles are so vigorously attritioned that wears the particle surface thus removing the iron stains therefrom, which may afterwards be eliminated from the sand particles preferably by high intensity magnetic separation.
Furthermore, the characteristics of said new abrasive-attrition step are so peculiar that said sand particles are so vigorously attritioned to each other under dry conditions or under lightly humid conditions, that pulverize independent aluminosilicate and other softer contaminant particles which are finally eliminated simply by washing and/or screening.
The process for purifying silica sand, in accordance with the present invention, simplifies in this way the process by reducing, to one, the number of the conventional attrition steps, suppresses the necessity of the chemical attack and consequently the consumption of water of said chemical attack and attrition step, because the process can now be carried out under dry conditions with 100% of solids or in the presence of 0 to 10% of water, considerably reducing the consumption of water of the whole process (at about 30%) when high degree of purity is required for the sand.